Hard disk drives typically include multiple disks that have a magnetic memory storage surface for storing data. A magnetic head including a read/write transducer passes over the disk surface for reading and writing data. The transducer must be precisely positioned on particular disk tracks in a consistent way to quickly and reliably read and write the data. In the disk drive industry, there is a trend to fit more and more disk tracks per unit of disk surface to maximize the disk storage capacity. Accordingly, precise positioning of the transducer with respect to the disk surface is critical.
Prior art hard disk drives have an E-block that pivots on a pivot bearing. The E-block has multiple actuator arms. Suspensions attach to the actuator arms to suspend the magnetic heads above the disk surface. The suspensions are typically spring loaded, having a particular gram load, to enable the heads to maintain a desired flying height just above the spinning disk surface. Changes in this gram load affect the flying height of the head.
Changes in the gram load are influenced by many factors. These factors include misalignment and deformation of critical components. For example, the suspension and actuator arm may misalign during assembly. The pivot bearing of the E-block may misalign within the E-block. Bearing and actuator arm defects may cause misalignment. Pivot bearing inner race runout, bore inaccuracies in the E-block, or bearing installation errors are examples of common causes for bearing and E-block misalignment that can result in gram load variations. The actuator arm tips may end up varying from a desired height and orientation, causing attached suspensions to have varying gram loads.
Often, gram load changes are associated with the process of attaching the suspension to an actuator arm. Swaging is the most common method of attaching the suspension to the actuator arm and involves pressing swage balls through the hub of a suspension baseplate. The swage balls expand the hub against the actuator arm to hold the suspension and actuator arms together. Pressing swage balls though the hub may distort the baseplate, changing the suspension gram load.
There are known ways of adhesively bonding a suspension to an actuator arm to overcome the undesirable effects of swaging. For example, a doughnut-shaped adhesive washer has been interposed between the actuator arm and the suspension hub. When the suspension hub inserts into the actuator arm opening, heat is applied to melt the washer and thereby create a bond.
There are drawbacks to known adhesive attachment methods. Heating the doughnut-shaped washer melts the washer. As the washer melts, it deforms. This deformation can allow the suspension to misalign relative to the actuator arm, changing the suspension gram load. Another drawback of the adhesive washer is that the hub locates relative to the actuator arm tip to create a bond. When the actuator arm tips misalign, the suspension will also misalign. There is no provision for correcting for actuator arm tip variations that cause gram load variations. What is desired is a way of correcting fabrication misalignment and distortion errors to maintain a consistent gram load.